The present invention generally relates to rotary transformer devices for 4-head type recording and/or reproducing apparatuses which carry out recording and/or reproduction by use of four rotary video heads, and more particularly to a rotary transformer device which performs transmission and reception of signals between the four rotary video heads and a recording and/or reproducing circuit.
Generally, an existing helical scan type recording and/or reproducing apparatus (VTR) records a video signal by rotary heads onto tracks which are formed obliquely to the longitudinal direction of a magnetic tape upon recording, and reproduces the recorded signal from the tape upon reproduction. Among this type of a helical scan type VTR, there is a known 4-head type VTR in which four rotary video heads are equally spaced apart and mounted on a rotary body such as a rotary drum and a rotary plate, so that adjacent rotary video heads are spaced apart by 90.degree.. In this 4-head type VTR, two mutually opposing rotary video heads have gaps of the same azimuth angle. In addition, the adjacent rotary video heads have gaps of mutually different azimuth angles. Certain conditions must be satisfied in order to form a tape pattern on the tape by the 4-head type VTR, so that the tape pattern is identical to a tape pattern which is formed on the tape by the existing VTR (hereinafter referred to as a 2-head type VTR) which carries out the recording and reproduction by use of two rotary video heads which are mounted diametrically on a rotary body. One condition which must be satisfied, is to select the azimuth angles of the gaps in the four rotary video heads to the same azimuth angles as the gaps in the two rotary video heads of the 2-head type VTR. Another condition to be satisfied, is to wrap the tape around the peripheral surface of the rotary body over an angular range of approximately 270.degree.. Still another condition which must be satisfied, is to select the tape traveling speed so that the tape travels by one track pitch during one field period in which one rotary video head rotates by 270.degree..
If the above conditions are satisfied, the length of the tape which is in contact with the peripheral surface of the rotary body in the 4-head type VTR, becomes equal to the length of the tape which is in contact with the peripheral surface of the rotary body in the 2-head type VTR. In addition, the relative linear speed between the tape and the rotary video head in the 4-head type VTR becomes equal to the relative linear speed in the 2-head type VTR. As a result, one field of the video signal is successively recorded on one video track by the four rotary video heads, and it becomes possible to form a tape pattern on the tape which is completely the same as the tape pattern formed by the 2-head type VTR. Therefore, a compatible tape pattern is formed so that perfect compatibility can be ensured between the 2-head type VTR and the 4-head type VTR.
When supplying the recording video signal to each of the four video heads and when supplying the video signals which are reproduced from the four video heads to a reproducing circuit in the 4-head type VTR, the transmission and reception of signals are performed through rotary transformers which are provided exclusively for the four video heads. Thus, a total of four rotary transformers are required. The four rotary transformers are made up from a stationary core and a rotary core which are mutually separated, four ring-shaped coils which are embeddedly provided in the stationary core, and four ring-shaped coils which are embeddedly provided in the rotary core so as to oppose the four ring-shaped coils in the stationary core. However, the diameter of the rotary body which is mounted with the four video heads in the 4-head type VTR, is smaller than the diameter of the rotary body which is mounted with the two video heads in the 2-head type VTR. Thus, the diameters of the stationary core and the rotary core which constitute a common part of the four rotary transformers, respectively become smaller than the diameter of the rotary body which is mounted with the four video heads. Moreover, four ring-shaped coils had to be provided in both the stationary core and the rotary core which have these small diameters. Consequently, the adjacent ring-shaped coils had to be arranged exceedingly close to each other.
In addition, a total of three video heads including one video head which is actually carrying out the recording or reproduction, simultaneously scan over the tape in the 4-head type VTR. Hence, reproduced signals from three video heads are simultaneously obtained through three rotary transformers during the reproducing mode of the 4-head type VTR. However, because the ring-shaped coils which constitute the four rotary transformers are arranged exceedingly close to each other as described above, there was a problem in that the reproduced signals from the two video heads which simultaneously scan over the tape together with the one video head which is actually carrying out the reproduction, may mix into the reproduced signal from the one video head as crosstalk in the rotary transformer which transmits this reproduced signal from the one video head.